Variables for SQL Server database

Declaring local variables
DECLARE @ variable name data type
DECLARE @name varchar (8)
DECLARE @seat int

Assign value
SET @ Variable name = value or
SELECT @ variable name = value

SET @name = ' Zhang San '
SELECT @name = studentname from Student WHERE studentno = ' 10011 '

The difference

SET SELECT
Support is not supported for assigning multiple variable values at the same time
An error when an expression returns multiple values assigns the last value returned to the variable
The variable is assigned a null value when the expression does not return a value the variable remains the original value

Variables for SQL Server database